Emulsions are mixtures of two or more incompletely miscible liquids such as oil and water. There are many kinds of emulsions in use in the modern world. Some, such as milk, mayonnaise, creams for foods, cosmetic creams and the like, are used in the home. Others, such as paints, adhesives, drugs, pesticides, asphalt and the like, are utilized in industry.
If an emulsion is left to stand without agitation for a long period, it will generally separate into its two or more constituent liquids by creaming, cohesion and coalescence of its dispersed droplets. It is therefore important for industrial use of emulsions to be able to evaluate their chemical stability as well as their mechanical properties such as hardness, fluidity and deformability.
Some emulsions such as cosmetic creams, nutrient creams and butters are not stable during the use, and the evaluation of such emulsions has conventionally depended on tactile tests conducted by skilled panalers. Although human sensitivity is very high and such evaluations are generally accurate, they involve some disadvantages. Specifically, they are strongly influenced by the panelers' physical condition, individual preferences, the test environment, and so on. Therefore the data sometimes vary widely and are not always reliable.